1. Field of the Invention
The present invention relates to a mobile communication system, and particularly, to an apparatus and method for automatically controlling a Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) terminal.
2. Background of the Related Art
Typically, in a mobile communication system, a base station performs uplink power control in order to solve a near/far problem in a cell and to maximize system capacity. The uplink power control can be divided into an uplink open loop power control and an uplink closed loop power control. A transmission power of a terminal in the uplink open loop power control is determined by an average of powers received by a base station through all Code Division Multiple Access (CDMA) channels. After performing the transmission initialization of the uplink channels through the open loop power control, the power control method is changed to the closed loop power control such that the transmission power of the terminal is determined by a power control signal received from the base station.
FIG. 1 shows a frame format adopted to a TD-SCDMA system. As shown in FIG. 1, a radio frame is subdivided into 2 subframes and each subframe is divided into a plurality of time slots. A transmit power control (TPC) symbol is transmitted to the mobile terminal once per 5 ms subframe and FIG. 1 shows a time slot TS4 having the TPC symbol, as an example. The mobile terminal controls the transmission power of itself based on the TPC received from the base station in a closed loop power control process.
Generally, the mobile terminal uses three types of automatic control signals to control a quality of transmission channel: an automatic power control (APC) signal for controlling transmission power, an automatic gain control (AGC) signal for controlling receiving power, and an automatic frequency control (AFC) signal for compensating for a small change of reference frequency. These automatic control signals are generated in a baseband modem of the mobile terminal under control of an upper layer application and transmitted to a transmission/reception (Tx/Rx) unit of an RF processing module.
FIG. 2 is a block diagram illustrating a related art automatic control apparatus for a TD-SCDMA transceiver, which comprises a baseband modem 20 and an RF processing module 10. Data received through an antenna is processed with a low noise amplifier (LNA), a mixer, an IF VGA, and an IQ decoder of the RF processing module 10, and transmitted to the baseband modem 20. In addition, the data to be transmitted is modulated by the baseband modem 20, transferred to the RF processing module 10, and transmitted through the antenna after being processed by the RF processing module 10 having an IQ coder, an IF mixer and the variable gain amplifier (VGA).
As shown in FIG. 2, the transmission data processed in a control unit 22 of the baseband modem 20 is transmitted to the Tx/Rx unit 12 of the RF processing module 10 through an ADC/DAC interface 25. The received data processed in the Tx/Rx unit 12 is transmitted to the control unit 22 of the baseband modem 20 through the ADC/DAC interface 25.
Also, the control unit 22 of the baseband modem 20 generates automatic control signals and transmits the signals to the RF processing module 10 through control lines 31, 32 and 33 which are additionally installed and used for the respective control signals. The control signals are generated in a pulse width modulation (PWM) method, and converted into DC signals by a low pass filter (LPF) 30 located between the RF processing module 10 and the baseband modem 20. Then, AGC and APC are transmitted to the Tx/Rx unit 12 and AFC is transmitted to an oscillator 17.
However, the related art automatic control apparatus has numerous disadvantages. For example, three signal lines are required for transmitting the respective control signals in addition to the data line. This makes a PCB wiring and routing design for the control signal more complex.
Also, since the automatic control signal is a PWM signal in the conventional automatic control apparatus, a filter for converting the PWM signal into the DC signal is required. Furthermore, since the filter consists of passive devices, it is difficult to integrate the filter in an IC chip, resulting in a corresponding increase of the apparatus size.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.